1. Field of the Invention
The present invention is related to a display apparatus, and more particularly, to a display apparatus capable of being viewed through a polarization component by users.
2. Description of Related Art
Since liquid crystal displays (LCDs) are not self-illuminating, an external light source is required for providing the LCD panels with enough brightness. LCDs can be classified into three types by different light sources, which are transmissive LCDs, transflective LCDs and reflective LCDs. Among them, the transflective LCDs utilizing both a back-light source and an external light source are suitable for being applied to portable products, such as cell phones, personal digital assistants (PDAs) and e-Books. Therefore, the transflective LCDs draw more and more attention from the public.
In a general-purpose LCD, an upper polarizer and a lower polarizer are usually disposed on an external surface of the LCD panel to achieve a display effect. However, when the LCD is applied to a portable product, a user wearing sunglasses usually can not clearly identify images displayed on the LCD due to the polarizers disposed therein.
FIG. 1A is a schematic view illustrating sunglasses and a conventional LCD. Referring to FIG. 1A, an LCD 100 includes a back-light source 110, an upper polarizer 120, a lower polarizer 130 and an LCD panel 140 disposed between the upper polarizer 120 and the lower polarizer 130. As shown in FIG. 1A, a transmittance axis of the upper polarizer 120 extends in a direction D1. Therefore, after passing through the upper polarizer 120, an image displayed on the LCD panel 140 has a polarization D1. When a user wears sunglasses 150 having a transmittance axis extended in a direction D2, the user can only view a portion of the light, which thus causes the brightness visible to the user to be decreased.
FIG. 1B is a coordinate graph depicting the polarization of the image displayed on the LCD in FIG. 1A and the transmittance axis of the sunglasses. In FIG. 1B, the X axis in the coordinate graph is defined as paralleling with a long edge of the LCD 100 and the Y axis in the coordinate graph is defined as paralleling with a short edge of the LCD 100. Referring to FIG. 1B, a component of the displayed image having the polarization D1 can be viewed by the user. The component is parallel to an extending direction D2 of the transmittance axis of the sunglasses 150. Thus, the brightness of the image viewed by the user significantly decreases. In addition, the displayed image having the polarization D1 is a linear polarized light, and thus, the component of the polarization D1 projected on the polarization D2 obviously varies with an included angle between the polarization D1 and the polarization D2. In other words, when the included angle between the transmittance axis of the sunglasses 150 and the polarization D1 is changed, the image viewed by the user obviously varies. Therefore, when the user wearing the sunglasses 150 views the LCD 100, a problem of high dependency on included angle between optical axes exists in the LCD 100 of prior art.
To solve the above-mentioned problem, another conventional technique is provided. FIG. 2A is a schematic view illustrating sunglasses and another conventional LCD. FIG. 2B is a coordinate graph depicting the polarization of an image displayed on the LCD in FIG. 2A and a transmittance axis of the sunglasses. Referring to FIGS. 2A and 2B, a quarter-wave plate 160 is disposed between the upper polarizer 120 of the LCD 100 and the sunglasses 150. When the displayed image of the LCD 100 passes through the quarter-wave plate 160, the polarization of the displayed image is converted from a linear polarized light to a circular polarized light. In comparison with the linear polarized light, the component of the circular polarized light is approximately the same in each direction. Thus, the above-mentioned problem of the LCD 100 can be mitigated.
However, the brightness in the scenario where the user wearing the sunglasses views the LCD still can not be effectively enhanced. Therefore, how to solve both the problems of brightness and the dependency on included angle between optical axes will be a key point of the development in the LCD application.